1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing a semiconductor device having a contact plug for wiring.
2. Description of the Related Art
Recently, in a semiconductor device, a contact hole has become miniaturized due to high integration, and it has been used a method for manufacturing such a semiconductor device in which a contact plug is formed by burying an electrically conductive material in the contact hole. Such a conventional method is conducted, for example, as follows.
First, as shown in FIG. 1A, a field oxide insulating film 302 is formed on a silicon substrate 301, and an n.sup.+ -type diffusion layer 303 doped with arsenic, etc. is formed on the substrate 301 in a selected area.
Next, as shown in FIG. 1B, on the substrate processed as in the above, an inter-layer insulating film 304 of silicon oxide and a patterned photoresist film 305 are formed in this order, and then a contact hole 306 is formed through the insulating film 304 by means of a photolithography and etching processes using the photoresist film 305 as a mask to expose the n.sup.+ -type diffusion layer 303. Thus, the contact hole 306 reaches the n.sup.+ -type diffusion layer 303.
Next, as shown in FIG. 1C, a polysilicon film 307 is deposited in the contact hole 306 and on the insulating film 304.
Next, an etching process is conducted to remove the polysilicon film 307 on the insulating film 304 and to leave the polysilicon film 307 in the contact hole 306. Thus, a contact plug 308 is formed in the contact hole 306 as shown in FIG. 1D.
Next, the contact plug 308 is doped with phosphorus by means of an ion implantation process, and a tungsten silicide (WSi.sub.x) film 309 is formed and patterned to form a wiring which is in contact with the contact plug 308.
A drawback of the above conventional method is an occurrence of "plug loss", in that the contact hole 306 is not completely filled by the plug 308. The reason is that, when conducting the etching process of the polysilicon film 307 to form the contact plug 308, an over etching is necessary in order to avoid the polysilicon film 307 to be left on the insulating film 304 and therefore, the polysilicon film 307 in the contact hole 306 is also etched in some extent. If a depth of the contact hole 306 is small, the substrate 301 is in danger of etching.
A further drawback of the conventional method is that an upper layer wiring becomes in danger of occurence of defects such as disconnection. The reason is that, when there is the plug loss, a step coverage of the upper layer wiring in contact with the contact plug 308 is lowered.